1. Field of the Invention
The present invention relates to a photosensitive resin composition. More particularly, the present invention relates to a photosensitive resin composition (particularly, photosensitive resin composition for flexographic printing) which can be developed with water, and at the time of development, the composition has small swell characteristics with water and small decrease in strength, is superior in resilience in spite of small change in dimension, and is superior in printability.
2. Description of the Prior Art
Various photosensitive resin compositions have been used in the fields of photoresist, printing ink, plate-making, etc.
As such a photosensitive resin composition, there have been known compositions containing a cyclized rubber and a bisazide compound; compositions containing a thermoplastic elastomer, an acrylic monomer and a photopolymerization initiator; and compositions mainly containing a photosensitive resin (e.g. polyester acrylate, epoxy acrylate, vinyl polycinnamate, chloromethylated polystyrene, aromatic azide group-containing resin, etc.). However, these photosensitive resin compositions are not water-soluble and an organic solvent is exclusively used at the time of developing. However, an influence of the organic solvent on the environment has recently become a serious problem, in addition to safety at the time of operating and about health hazards.
Therefore, a photosensitive resin composition capable of alkaline developing, comprising a novolak resin or poly(vinyl phenol) and a quinone diazide compound, is known to solve the above various problems, but a photosensitive resin composition capable of water developing, which is more safe and simple, is desired.
As the water-developing photosensitive resin composition, for example, there are suggested a composition comprising a water-soluble resin as a main component, such as a composition comprising a water-soluble resin (e.g. polyvinyl alcohol, gelatin, casein, etc.), bichromate salt and diazonium salt or bisazide compound, and a composition comprising a water-soluble resin, a water-soluble acrylic monomer and a photopolymerization initiator, etc.
However, regarding a conventional water-developing photosensitive resin composition, the hydrophilic nature of the resin as the main component in water is remarkable. Therefore, the resin composition swells at the time of developing to cause a decrease in strength and a change in dimension. As a result, the dimensional accuracy of the resist, printing durability of the printing plate (plate wear) and printing quality are deteriorated.
In order to solve the problem of these water-developing photosensitive resin compositions, there is suggested a photosensitive resin composition obtained by formulating a photopolymerizable unsaturated monomer, an amino group-containing compound and a photopolymerization initiator with a copolymer comprising a conjugated diene compound or an acrylic ester compound, an .alpha., .beta.-ethylenic unsaturated carboxylic acid and a polyfunctional vinyl compound, said copolymer being soluble in an aqueous alkaline solution (e.g. Japanese Laid-Open Patent Publication Nos. Sho 60-179411, Sho 60-219208 and Sho 61-181811).
In addition, as another water-developing photosensitive resin composition, a composition comprising a partially crosslinked copolymer of an aliphatic conjugated diene, an .alpha., .beta.-ethylenically unsaturated carboxylic acid and a polyfunctional vinyl compound, an aliphatic conjugated diene copolymer having a molecular weight of not less than 5,000, a photopolymerizable unsaturated monomer, a basic nitrogen atom-containing compound and a photopolymerization initiator (e.g. Japanese Laid-Open Patent Publication No. Hei 1-300246, etc.); a composition comprising a polymer having a tertiary amino group and a polymerizable unsaturated group, an .alpha., .beta.-ethylenicunsaturated monomer having a free acid group, a photopolymerizable unsaturated monomer and a photopolymerization initiator (e.g. Japanese Laid-Open Patent Publication No. Sho 61-246742, etc.); and a composition comprising a photopolymerizable unsaturated monomer, an amino group-containing compound (a part of the photopolymerizable unsaturated monomer or amino group-containing compound has a (meth)acryloyl group) and an aromatic ketone and, optionally, an additional polymer (e.g. Japanese Laid-Open Patent Publication No. Sho 61-228002, etc.) are known.
However, these photosensitive resin compositions are not satisfactory in balance between characteristics such as water-developing properties, flexibility after photosetting and developing, resilience, hardness of rubber, mechanical strength, etc.